1. Field of the Invention
This invention relates generally to industrial straight lock stitch sewing machines, especially to a thread trimming device for a sewing machine in which an upper thread and a lower thread are subject to being caught by a thread catcher and trimmed by cutter blades after the termination of the sewing operation.
2. Description of the Prior Art
A thread trimming device of this class is disclosed, for example, in U.S. Pat. No. 3,921,554, patented Nov. 25, 1975 in which a first partial gear fixedly secured to a first shaft connected to a hook shaft meshes with a second partial gear disposed on a second shaft which is operably connected to a thread catcher through a clutch against the action of a spring to move the second shaft for thread trimming operation. However, high compressive pressure is applied between a holder of the thread catcher and a metal bearing for the shaft by virtue of trimming pressure applied when trimming the thread, thereby precluding smooth sliding of the second partial gear during the trimming operation and further swivel of the thread catcher and the holder thereof returning to the original position after the termination of the thread trimming operation.